12.02.3 Drugs to Prevent an Attack of Typical Angina

Three groups of drugs are used to prevent attacks of typical angina; the nitrovasodilators, the β-adrenoceptor blockers (such as metoprolol and atenolol) and Ca²⁺ channel blockers. Verapamil is the Ca²⁺ channel blocker used in an attack of angina, as it has a more pronounced effect on the heart than on the blood vessels. Like nitrovasodilators, b-adrenoceptor blockers and Ca²⁺ -channel blocker decrease the work done by the heart/O₂ demand to levels that can be met by the diseased coronaries.

The nitrovasodilators used to prevent attacks of typical angina are nitroglycerin patches, which are applied topically to provide slow release of the nitrovasodilators. As isosorbide mononitrate has no significant first pass liver metabolism, it can be used orally to prevent angina attacks.

Long term treatment with nitrates is associated with tolerance (reduced effect) to nitrates for which the mechanism is unknown. To prevent this reduced effect, drug holidays are used to prevent tolerance from developing. This can be achieved by not applying the patch or ointment overnight.

Both β-adrenoceptor antagonists and the Ca²⁺-channel antagonist verapamil interrupt the process in an attack of typical angina. In the stable form of typical angina, exercise or stress provoke an attack by increasing the activity of the sympathetic nervous system and hence the release of noradrenaline, which acts at the cardiac β₁-adrenoceptors to increase the heart rate and force, and the work done by the heart, which increases the oxygen demand to above that supplied in the diseased coronary arteries (Table 12.2.1). β-adrenoceptor antagonists inhibit the binding of the noradrenaline to the cardiac β₁-adrenoceptors to decrease the heart rate and force, and the work done by the heart, which decreases the oxygen demand to that supplied in the diseased coronary arteries to end the attack of angina (Table 12.2.1).